Socially and professionally, most people rely upon video displays in one form or another for at least a portion of their work and/or recreation. With a growing demand for large screens, such as high definition television (HDTV), cathode ray tubes (CRTs) have largely given way to displays composed of liquid crystal devices (LCDs), plasma display panels (PDPs), or front or rear projection systems.
A CRT operates by scanning electron beam(s) that excite phosphor materials on the back side of a transparent screen, wherein the intensity of each pixel is commonly tied to the intensity of the electron beam. With a PDP, each pixel is an individual light-emitting device capable of generating its own light. With an LCD, each pixel is a back-lit, light modulating liquid crystal device.
As neither system utilizes a large tube, LCD and PDP screens may be quite thin and often are lighter than comparable CRT displays. However, the manufacturing process for LCDs, PDPs and most other flat panel displays is much more complex and intensive with respect to both equipment and materials than that of CRTs, typically resulting in higher selling prices.
Projection systems offer alternatives to PDP and LCD based systems. In many cases, projection display systems are less expensive than comparably sized PDP or LCD display systems. Rear projection display systems typically employ a wide angle projection lens (or multiple lenses), operating in connection with one or more reflective surfaces to direct light received from the projector through the lens(es) to the back of a screen. The lens and mirror arrangement typically enlarges the image as well. To accommodate the projector, one or more lenses, and reflectors, rear projection displays are typically 18 to 20 inches deep and as such may not be suitable for on-wall mounting in some environments.
Often, rear projection display devices exhibit average or below average picture quality in certain environments. For example, the brightness and contrast of the images on the rear projection displays may be degraded substantially off axis or when lighting conditions vary within the environment. Light output and contrast is a constant issue in most settings and viewing environments.
A display may also have to contend with two types of contrast—dark-room contrast and light-room contrast. Dark-room contrast is simply the ratio between the intensity of light and dark image objects with minimal ambient illumination such as in a controlled dark room with black walls, ceiling, floor and furniture. Light-room contrast is similarly the ratio between the intensity of light and dark image objects in a lighted environment, such as a living room illuminated with typical household lighting fixtures or at daytime.
Front projection systems typically use a screen to reflect incident light back toward an observer. A typical front projection screen usually reflects equally well the light from the imaging source and the ambient light. They provide good dark-room contrast where ambient light is low but are subject to poor light-room contrast due to the interference of ambient light. Specifically, ambient light incident upon the screen may be reflected back to the viewer and thus compete with the intended image. In a room with well designed illumination intended to provide a uniform lighting level, the ambient illumination raises the illumination intensity on the screen more or less uniformly and thus reduces the contrast and perceived quality of the intended image.
Rear projection displays and emissive displays such as LEDs, LCDs and PDPs typically provide better light room contrast than front projection systems. Fabrication and material costs tend to make these emissive displays more costly then projection display systems. Rear projection systems are typically more complex than front projection systems. This complexity typically translates into a higher sales price as well.
Weight, thickness, durability, cost, aesthetic appearance, and quality are key considerations for display systems. Hence, there is a need for a device that overcomes one or more of the drawbacks identified above.